Travelling-wave motor

ABSTRACT

A travelling-wave motor utilizes a flexible travelling waves generated in a stator for driving a rotor. The stator has an elastic vibrating body and a ceramic piezoelectric vibrator provided on one side of the elastic vibrating body. The central portion of the vibrating body is locked and supported on a central axis provided on a ground way. An output extracting projection for driving inside of the outermost periphery of the vibrating body on the one of the vibrating body and the rotor to press and contact with each other. The vibrating body and the piezoelectric vibrator is excited radially in a primary vibration mode.

BACKGROUND OF THE INVENTION

This invention relates to a travelling wave motor, e.g. a compactultrasonic motor using ultrasonic oscillation and having anelectro-mechanical transducer for generating a travelling-wave and amovable member driven by the travelling wave.

One known ultrasonic motor is a standing-wave type motor which employs aLangevin oscillator as a driving source. Such a motor is disclosed inU.S. Pat. No. 4,019,073. Another known ultrasonic motor is atravelling-wave type motor employing a travelling wave generated on astator for driving a rotor provided on the stator. The travelling-wavemotor generates smaller wear in the friction-transmission surfacebetween the stator and the rotor, and can more easily be driven in thereverse rotation direction by comparison with the standing-wave typemotor. Such a travelling-wave motor is disclosed in U.S. Pat. No.4,513,219 (Katsuma et al), U.S. 4,562,374 (Sashida) and EP-A-169,297(Tokushima).

FIG. 2 represents one example of a traveling wave generation principle,in the travelling-wave motor. A reference numeral 1 denotes apiezoelectric transducer consisting of piezoelectric ceramic,piezoelectric crystal, which is polarized at equal intervals by a widthb with the adjacent polarizations opposite each other in direction asillustrated. An electrode 2 is formed on each piezoelectric transducerthrough evaporating or plating a conductive material such as silver,nickel or the like, and these electrodes are connected by signal lines10, 11 each to have a high frequency voltage impressed thereon from adifferent signal source. Then, a void c in width is provided betweenelectrode groups connected by the signal lines 10, 11 each. In thiscase, the void c in width may have nothing of presence of thepolarization and the electrode. Here, the distance between centers ofthe electrodes across the width c will be denoted by a for theconvenience of description. A mechanism of the travelling wavegeneration will be described with reference to FIG. 2 and referencecharacters given therein. An inflected vibration wave consisting oftravelling wave and regressive wave may be expressed by the followingequation from taking the midpoint of an electrode portion as areference.

    Asin(ωt-kx)+Asin(ωt+kx)                        (1)

Here, (a) indicates a so-called standing wave. Then, an inflectedvibration wave on an electrode portion may be expressed as follows.

    Bsin{ωt-k(x+a)+φ}+Bsin{φt+k(x+a)+φ}      (2)

were k=ω/ν=2π/λ

λ:wavelength,φ:phase difference angle

In Eq. (2), where ##EQU1## then Eq. (2) may be expressed as:

    Bsin(ωt-kx+απ)+Bsin(ωt+kx+βπ) (4)

Accordingly, the inflected vibration wave excited by ○1 , ○2 may beexpressed in a type having Eqs. (1) and (4) put together. Here, if acondition for the presence of a traveling wave only is considered fromthe development of Eq. (4), it is understood that it comes in the casewhere is an even number and β is an odd number. Here, is φ expressed byequations of α and β may be given as follows from Eq. (3). ##EQU2## Thatis, when (α,β)=(0, 1), (2, 3), a=λ/4, φπ/2, when (α, β)=(2, 1), a=λ/4,φ=3/2π, when (α, β)=(0, 3), a =3/4λ, φ=3/2, and thus the travelling wavecomponent only is present when a and φ are satisfied each concurrently.If, for example, the case where a=3/4λ, b=λ/2 and φ=3/2π, is considered,then Eq. (1)=Eq. (2) will be:

    Asin(ωt-kx)+Asin(ωt+kx)+Bsin(ωt-kx)- Bsin(ωt+kx)(6)

Here, if amplitudes A and B of a high frequency voltage signal generatedfrom a driving circuit are A=B, then Eq. (6) will be 2Asin(ωt-kx), andthus it is understood that the travelling wave component only remains.Further, for reversing drive the regressive wave component only will bemade to remain, therefore and β in Eq. (5) will be inverted, thus α andβ being odd and even respectively. When considered with reference to ○1practically, a phase of the signal to be applied to ○2 may be shifted180° as compared with the case of forward drive.

FIG. 3 represents a principle on which the travelling-wave motor runsaccording to a travelling wave component. A reference numeral 3 denotesa vibrator part, which may generate an inflected vibration as thepiezoelectric vibrator is bonded to an elastic member. Now, when atravelling wave is generated rightward on the principle shown in FIG. 2,one spot on the surface of the vibrator part 3 draws a leftward ellipticpath, therefore a rotor part 6 moves counter to the direction in whichthe travelling wave goes. The above is so reported in NIKKEI MECHANICAL(Sept. 23, 1985) and others, and a detail description on one spot on thesurface of the vibrator part 301 drawing an elliptic path is also giventherein.

Katsuma et al. and Sashida disclose a travelling-wave motor employing aLing type piezoelectric member. FIG. 4 shows one of this typetravelling-wave motor. This type of travelling-wave motor essentiallyconsists of an annular vibrating body 403 and movable body 405 providedthereon. The vibrating body has as annular piezoelectric vibrator 404thereon. The vibrating body 403 is fixed to a base 402 through asupporting mechanism 406. On the annular piezoelectric vibrator, a gaphaving a length of half of the arc of an electrode is provided betweentwo electrode groups. The travelling wave is brought about by applyingan AC signal having a phase difference of 90° to the two groups.

Another type of travelling-wave motor employing a disk-shapedpiezoelectric member is disclosed in the European Patent of Tokushima.FIG. 5 shows this type of travelling-wave motor. In the figure a statoris constituted by a disk-shaped resilient vibrating body 503 having atoothlike circular projection. The vibrating body 503 has a disk-shapedpiezoelectric vibrator 504 thereon. A movable body 505 is provided onthe projection of the vibrating body and has a central shaft to act as arotational guide. A pressure-regulating device is provided on thecentral shaft for effecting a suitable contact pressure between thevibrating body and the movable body so that the travelling wavecomponent can be efficiently transmitted to the movable body. Thevibrating body is supported and fixed on two circular projections formedon a base. The disk-shaped piezoelectric vibrator consists of aplurality of electrodes arranged in such a manner that an electrodepattern 601a divided at equal intervals is provided on almostsemicircular portion of one side plane of it as shown in FIG. 6 and anelectrode pattern 601d divided at equal intervals likewise is providedon remain almost semicircular portion through blank areas 601b and 601cleft in 0.5 pitches and 1.5 pitches on opposite end portions. Thepiezoelectric vibrator is polarized so that the adjacent electrodepatterns is in the counter direction.

For mounting in this case, almost semicircular metallic plates, forexample, are bonded conductively at every almost semicircular electrodeblocks to homopolarization electrically, and signals 90° different inphase are impressed thereon through two lead wires, thereby generating atravelling wave.

In a travelling-wave motor of the type described above, if itsconstruction includes an annular vibrating body, the travelling wave issignificantly damped to a certain degree due to the required supportingstructure since the flexure mode travelling wave which has been excitedby the piezoelectric vibrator has no nodal point of oscillation. As aresult of this, the electro-mechanical transducing efficiency is low.

If the construction of the travelling-wave motor includes a disk-type ofvibrating body, there is the advantage that the vibrating body can befixed and supported by the base at two places in the radial direction ofthe base because the vibrating body is excited in a secondaryoscillation mode in the radial direction of the vibrating body, however,in the case of a thin and small sized travelling-wave motor which is anobject of the invention, a deterioration of efficiency is also quiteunavoidable according to a dispersion of node positions and dimensionsof the supporting area and force, and since a driving frequency exceeds100 kHz for excitation in the secondary vibration mode, a deteriorationof circuit efficiency may result.

If the piezoelectric element having the electrode patterns shown in FIG.4 is used, one standing wave is excited on one semicircular portion, astanding wave 90° different in phase therefrom is excited on the othersemicircular portion, the standing waves different each other arepropagated to the semicircular portions on the counter side mutually,and the two standing waves are thus synthesized to generate a travellingwave, therefore a source for generating the two standing waves comesone-sided to the semicircle, and thus a uniform travelling waves cannotbe excited. As one quantitative data indicating such phenomenon, forexample, some peaks called "sprious" peaks can be observed other than arise at the resonance point in frequency-amplitude characteristics.Consequently, an electric-mechanical transduce efficiency of the motordetoriorates.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide atravelling-wave motor having a thin shape and small diameter.

It is another object of the present invention to provide atravelling-wave motor with a low electricity consumption.

It is a further object of the present invention to provide atravelling-wave motor which has a high electrical-mechanical translationefficiency.

It is a still further object of the present invention to provide atravelling-wave motor which is driven by low driving frequency signals.

It is yet a further object of the present invention to provide atravelling-wave motor in which an amplitude of the vibrator is lessattenuated as compared with the prior art structure.

These and other objects of the invention are accomplished by atravelling-wave motor utilizing flexible travelling waves generated in avibrating body for driving a movable body comprising a ground way forfixing the travelling motor, the ground body way having a supportingmeans, a vibrating body secured and supported in such a manner that thevibrating body is integrated with the supporting means, a piezoelectricvibrator secured to one side of the vibrating body for excitingtravelling waves in a primary oscillation mode with respect to theradial direction in the vibrating body, a movable body provided on thevibrating body, an annular projection provided on the one of thevibrating body and the movable body so that the vibrating body comesinto contact with the movable body through the projection at a portioninside of the outermost periphery of the vibrating body, and apressure-regulator provided on the movable body for generating suitablecontact pressure between the movable body and the vibrating body. Thesupporting means may be constituted by a support shaft which acts as acenter of rotation of the movable body. The pressure-regulator may befixed to the shaft. The annular projection may be provided on themovable body. The annular projection may include a toothed displacement.The movable body may have another annular projection at the contactposition with the projection of vibrating body. The breadth of theannular projection of the movable body may be narrower than that of thevibrating body. The thickness of the vibrating body at a position insidethe annular projection may be thinner than that at a position outsidethe annular projection. The supporting means may be made from aconductive material. The piezoelectric vibrator may be formed in a diskshape and has a central hole. The piezoelectric vibrator may haveelectrode patterns thereon. The electrode patterns may include aelectrode pattern divided into a plurality of divided electrode at equalintervals by multiple of 4 and two short circuit patterns forshort-circuiting so that the divided electrode are alternately connectedwith the short circuit patterns to form two sets of electrodes. Thepiezoelectric vibrator may be polarized so that every portions on whichone group consisting of two adjacent divided electrodes are formed arepolarized alternately into positive and negative potential. Thepiezoelectric vibrator may have a circular blank portion at theoutermost periphery thereof. The piezoelectric vibrator may have acircular blank portion at the periphery of the central hole. One of thedivided electrodes may have a marking pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 longitudinal sectional view of a travelling-wave motor relatingto the invention.

FIG. 2 is a principle drawing of a travelling wave generation.

FIG. 3 is a principle drawing of a travelling-wave motor rotation.

FIG. 4 and FIG. 5 are longitudinal sectional views of a prior arttravelling-wave motor.

FIG. 6 is plan view showing an electrode pattern for a piezoelectricelement of a prior art travelling-wave motor.

FIG. 7(a) is a partial sectional view representing amplitude measuringpoints.

FIG. 7(b) is a drawing representing the relationship between theamplitude measuring points and the amplitude when the vibrator part ismade from stainless steel.

FIG. 7(c) is a drawing representing the relationship between theamplitude measuring points and the amplitude when the vibrator part ismade from brass.

FIG. 8(a) is a partial sectional view representing output extractingpositions.

FIG. 8(b) is an explanatory drawing representing a difference of outputextracting position when the vibrator part is made from stainless steel.

FIG. 8(c) is an explanatory drawing representing a difference inamplitude of a vibrator due to a difference of output extractingposition when the vibrator part is made from brass.

FIG. 9 is a plane view showing an electrode pattern for a piezoelectricelement.

FIG. 10 is a plane view showing another electrode pattern for apiezoelectric element.

FIG. 11 is a plane view showing another electrode pattern forpiezoelectric element.

FIG. 12(a) is a plane view showing a reverse side electrode pattern fora prezoelectric element.

FIG. 12(b) is a plane view showing another electrode pattern for apiezoelectric element.

FIG. 13 is a plane view showing another electrode pattern for apiezoelectric element.

FIG. 14(a) is a plane view showing evaporated divided electrode patternsbefore polarization process.

FIG. 14(b) is a plane view showing evaporated divided electrode patternsafter polarization process.

FIG. 15 is a longitudinal sectional view of another travelling-wavemotor relating to the invention.

FIG. 16(a) is a plane view showing a vibrator part.

FIG. 16(b) is a sectional view showing a vibrator part.

FIG. 17 is a longitudinal sectional view of another travelling-wavemotor relating to the invention.

FIG. 18 is a diagram showing a relationship between the appliedfrequency and the impedance.

FIG. 19 is an equivalent circuit diagram of the travelling-wave motor.

FIG. 20 is a diagram showing a relationship between the appliedfrequency and the rotation frequency.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a longitudinal sectional view of a travelling-wave motorrelating to the invention. A central support rod 1 is unified with aground way 2 through screwing or driving, and further a vibrator part 3is unified in structure with the central support rod at the centralportion. In this case, the vibrator body 3 consists of an elastic membersuch as stainless steel, brass, duralumin or the like and is supportedsubstantially on the central support rod 1 at the central portion. Then,a mechanical resonance frequency of the central support rod 1, theground way 2 is sufficiently higher than that of vibrator body 3,piezoelectric transducer 5 and others, and the structure is thatvibration leakage and attenuation will almost not arise due to aninfluence of the support. The piezoelectric transducer 5 is apiezoelectric ceramic of at least one or more with a hole provided atthe center or a piezoelectric ceramic consisting of several segmentsdivided around, and that of having several patterns of electrodesprovided around to polarization is joined on a counter side to thesurface of the vibrator body 3 where an output extracting position 4 isprovided. The central support rod may consist of a conductive materialsuch as a metal. In such case, the back electrodes provided on the backside contacting with the vibrator body is electrically contacted withthe central support rod through the vibrator body. With the centralsupport rod 1 as a guide for the center of rotation, a moving body 6 isdisposed so as to come in contact with a portion of the outputextracting position 4 set on the vibrator body 3 by a pressureregulating spring 7. In this embodiment, the pressure regulating spring7 is platelike and set at a portion other than the ground way 2 or thetravelling-wave motor relating to the invention, and is arranged so asto apply pressure to a projection provided at the central portion of themoving body 6. In this case, if a pressure generated on the moving body6 by the pressure regulating spring 7 is N, a friction factor betweenthe vibrator body or part 3 and the moving body 6 is M, and a distancefrom the center of the vibrator part 3 to the output extracting position4 is a, then a torque T arising on the moving body 6 may be T=MNa or so.The output extracting position 4 is set so as to translate aninfinitesimal flexural vibration amplitude of the travelling wavecomponent excited by the vibrator consisting of the vibrator part 3 andthe piezoelectric transducer 5 efficiently into a rotational motion ofthe moving body 6, which may be realized by providing a projectionwhereby the vibrator part 3 and the moving body 6 are brought intocontact with each other only at one least one of the vibrator part 3 orthe moving body 6. In this embodiment, the projection comprises acircular protrusion 8 is provided on the moving body 6 so as to contactwith the vibrator body 3 at the output extracting position 4.

Generally a component of the elliptic path produced by a travelling wavewhich contributes to a rotation of the moving body has a speeddifference and a phase shift in the circumferential direction at eachposition radially of the vibrator part 3, therefore these factors leadto braking of the rotational motion of the moving body 6 resultingly asan auto-rotation component. Accordingly, it is preferable that aflexural vibration be extracted by providing the output extractingposition 4 radially at a part of the vibrator part 3 or the moving body6 as described above. Meanwhile, what is most characteristic of theinvention is the output extracting position 4. That is to say, in thefield of relatively small size and low power consumption, thetravelling-wave motor relating to the invention is of small structure,therefore the mechanical resonance frequency of the vibrator becomesinevitably high. Generally, a frequency exceeding 100 kHz may leadfinally to a deterioration of circuit efficiency of the driving system,therefore if the number of waves arising around the vibrator is 2 to 4,it must be excited by a primary vibration mode radially. When excitedpractically on the driving frequency working to be the primary vibrationmode, the amplitude gets larger as it gets nearer to the outsidediameter and is maximized at the outermost periphery. Accordingly, it isconceivable that the output extracting position be set at the outermostperiphery of the vibrator, whereat the moving body 6 may be brought intocontact therewith, however, if the moving body 6 is brought into contactat the amplitude-maximized position, a general amplitude of the vibratorwill practically be attenuated to an extreme, thus obtaining only suchrotational motion as is weak in torque at best. That is, a pressure bythe pressure regulating spring 7 cannot be set high, and the motorefficiency comes to a low value. On the other hand, the closer theoutput extracting position 6 is set to the inner periphery, the less anamplitude arising on the vibrator is attenuated, however, if it is setso consciously of the central axis, then since the amplitude itself atthe portion is small, only a weak rotational motion may result, too.Accordingly, if the radius of the vibrator part 3 is r, there existssome optimum value in the relation with the distance a from the centerto the output extracting position 4. Then, in the case of a vibrator 5mm in radius and 1 mm or below in thickness, the optimum value variesaccording to the diameter of the central axis support rod 1, however, itis set preferably at about 2/5r≦a≦4/5r for the motor efficiency. Adetailed description will be given thereof hereinlater.

As described above, when exciting at a driving frequency whereat thevibrator part 3 and the piezoelectric transducer 5 get in a primaryvibration mode radially, it is desirable that the output extractingposition 4 for driving the moving body 6 frictionally be set at aportion inward rather than the outermost periphery of the vibrator part3 for better efficiency of the motor. Then, in the embodiment, the casewhere the projection 8 working at the output extracting position 4 isset on the moving body 6 side, and the diameter of the moving body 6 maybe smaller than the outside diameter of the vibrator part 3 andsubstantially larger than the distance a.

FIGS. 7(a) to 7(c) indicate a radial behavior of the travelling-wavemotor relating to the invention, wherein FIG. 7(a) is a fragmentarylongitudinal sectional view of the travelling-wave motor relating to theinvention, indicating amplitude measuring portions different in positionradially as A, B and C. For amplitude measuring method practically,since the travelling-wave motor of the invention is thin and small insize, and an influence of dead weight of the contact type displacementmeter cannot be neglected, an optical non-contact type displacementmeter is used. FIGS. 7(b) and (c) diagram amplitudes measured at eachradial point of A, B and C with a travelling wave excited on a vibratorpart 3 and a piezoelectric transducer 5. Curves are obtained in thiscase with the number of waves excited in the circumferential directionas 3, outside diameter and thickness of the vibrator part 3 and thepiezoelectric transducer 5 as 10 mm and 0.3 mm respectively, and avibration voltage set at 3Vo-p and 10Vo-p in two ways. FIG. 7(b)indicates the case where the vibrator part 3 is of stainless steelmaterial, a radial primary mechanical resonance frequency being about 45kHz, and FIG. 7(c) indicates the case where the vibrator part 3 is ofbrass material, a radial primary resonance frequency being about 39.5kHz. From comparing FIG. 7(b) with (c), it is understood that a radialdisplacement distribution gets progressively larger as it comes near tothe outer periphery generally and is maximized at the outermostperiphery.

FIG. 8(a) to 8(c) indicate a disparity in amplitude of the vibrator dueto a difference in the output extracting position, illustrating adisparity in amplitude of the vibrator part due to a difference inposition whereat the vibrator part and the moving body come in contactwith each other. As in the case of FIG. 7(a), FIG. 8(a) is a fragmentarylongitudinal sectional view of the travelling-wave motor relating to theinvention. With portions A, B and C different in position radially asoutput extracting positions and the moving body coming in contactsubstantially with a vibrator part 3 only at portions A, B and C, eachfrequency characteristic of the vibrator was measured. That is, strapprojections which come in contact with each position of A, B and C areset on the moving body, and each moving body is remounted successivelyon the vibrator part 3, thereby comparing attenuations of the vibratoramplitude. The dead weight of the moving body is 0.3g in this case. Apiezoelectric transducer 5 being constituted of two circuits, the methodfor measuring frequency characteristics of the vibrator amplitudecomprises a technique wherein a cycle voltage is swept to ignition onone circuit, thereby subjecting the vibrator to a standing waveexcitation, and a back electromotive force generated on the othercircuit side according to a piezoelectric effect is subjected to Fourierconversion by a spectrum analyzer. FIGS. 8(b) and (c) diagram anattenuation mode of the amplitude near a mechanical resonance point ofthe vibrator by remounting successively the moving bodies coming incontact only with each position of A, B and C through the aforementionedtechnique practically. Forms of the vibrator part 3 and thepiezoelectric transducer 5 are the same as those of FIG. 7 in this case,and the impressed voltage is 5Vo-p.

FIG. 8(b) represents the case where the vibrator part 3 is of stainlesssteel material, and (c) represents the case where it is of brassmaterial as in the case of FIG. 7. From comparing FIG. 8(b) and FIG.8(c), it is understood that B is less in the maximum amplitude at aresonance point than A, and C is less than B regardless of thematerials. That is, the attenuation increases more and more according asthe position whereat the moving body contacts the vibrator part comesnear to the outer peripheral portion. The character E in the drawingsindicates a frequency characteristic of the vibrator which is examinedwithout mounting the moving body thereon, representing the maximumamplitude. However, there is no distinction observed between A and E aslong as the moving body weighing 0.3g or so is mounted, and a contact ofthe moving body at the position A is also to obtain an amplitude in thestate where the vibrator is almost free.

Now, in synthesizing the results of FIGS. 7 and FIGS. 8 , when thetravelling-wave motor relating to the invention is excited at a drivingfrequency working as a primary vibration mode radially, the amplitudeprogressively increases as it comes near to the outer periphery,however, when the moving body is disposed so as to come in contact onlywith the outer peripheral portion to the contrary, the amplitudeattenuation increases, which is disadvantageous. That is, it can be saidthat an optimum value may lie in the output extracting position wherethe moving body and the vibrator part come in contact. Then, consideringthat the attenuation becomes excessive from setting the value at theoutermost periphery but minimized, to the contrary, when it is set atthe innermost periphery, and that unless about 1/5 of the portion fromthe center to radius r is supported on the central support rod 1 for themotor structure, something disadvantageous may result in strengthagainst pressure applied by the moving body, it is preferable that theoutput extracting position from the vibrator to the moving body be setat about 2/5r≦a ≦4/5r. In consideration physically of the abovephenomenon, vibrations of the vibrator part and the piezoelectricvibrator in a free state at the portion will be effective in minimizingthe attenuation of an infinitesimal elliptic vibration generated on thesurface of the vibrator part, which may be translated into a rotationalmotion of the moving body. Then, an optimum position may be decided onthe output extracting position according to the outside diameter andthickness of the vibrator part and the piezoelectric transducer anddifference in pressure of the moving body, however, the value will beset at 2/5r≦a≦4/5r, and thus a high efficiency and smooth rotationalmotion may be realized even at low voltage on the travelling-wave motorrelating to the invention.

According to the aforementioned construction, since the primaryvibration mode is utilized diametrically of the vibrator part, a drivingfrequency can be lowered, and as the moving body is pressed andcontacted at the output extracting position set on a portion inside ofthe outermost periphery of the vibrator part, an amplitude of thevibrator part is less attenuated as compared with the case where themoving body is brought into contact with an outer peripheral portion ofthe vibrator part which is a displacement-maximized portion, thustranslating efficiently into a rotational motion of the moving body.

Further, the vibrator part is locked and supported at the center thereofso as to be integral with the central support rod, therefore even suchthin and small-sized vibrator part can stably and easily be supportedwithout attenuating the travelling wave in most cases.

FIG. 9 and FIG. 10 are plan views showing an electrode pattern of thepiezoelectric transducer for travelling wave excitation, indicating aconcrete electrode pattern of the piezoelectric transducer joined on oneside of the travelling-wave motor relating to the invention and capableof realizing a travelling wave excitation.

FIG. 9 shows segmentary electrodes 9a to 9d provided on one side of apiezoelectric vibrator 5 provided with a hole at the central portion,and an arc length of each electrode is set to be almost 1/4 of anexcited travelling wavelength including a clearance between the adjacentelectrodes. With a polarization applied as illustrated, the same signalis impressed to 9a and 9c and a signal shifting 90° in phase isimpressed to 9b and 9d, thereby exciting the travelling wave. Then, asmentioned hereinbefore, since the arc length of each electrode is 1/4wavelength, 1 wavelength is formed of 4 portions of 9a to 9d.Accordingly, the embodiment represents the case where the number ofwaves is 3. A reference character + in the drawings indicates that aplus field is applied to the electrodes on the back to polarization, andthat of - indicates that a minus field is applied to the electrodes onthe back to polarization. In this case, the back electrodes may be thesame-positioned and same shaped electrodes as the front electrodes orwholly covering electrode.

FIG. 10 illustrates another electrode pattern, wherein segmentaryelectrodes 9a to 9d are provided on the surface of a piezoelectrictransducer 5 having a hole at the central portion, and electrodes 15a to15d corresponding to almost 1/2 length of arcs of the electrodes 9a to9d are provided between the electrode ends. Here, a polarization isapplied as illustrated, and when high frequency voltages different inphase are inputted to each electrode of 9a to 9d according to the ruleshown in FIG. 2, the travelling wave component will be excited. In thiscase, another group of electrodes 15a to 15d can be utilized forfrequency tracking and speed variation of the travelling-wave motor withlevel and phase of the counter electromotive voltage generated at thetime of vibrator part excitation for detection as detection signals, andalso utilized for driving when a spurious vibration generated at thetime of vibrator part excitation is microscopic, thereby intensifyingthe travelling wave component.

FIG. 11 represents another electrode patterns for a piezoelectricelement used on a travelling-wave motor according to the invention,wherein segmentary electrode patterns 9a to 9d divided at equalintervals in the circumferential direction are formed on one side planeof the piezoelectric element 5 having a hole at the center, then theadjacent two patterns 9a to 9d are polarized in the same direction andthe next two patterns 9c and 9d in the counter direction as illustrated,and after polarization an electrode pattern 9e along the outer peripheryfor short-circuiting 9a and 9c and an electrode pattern 9f along theinner periphery for short-circuiting 9b and 9d are formed. Forelectrical polarity, two different electrodes such as outer peripheryshort-circuiting electrode and inner periphery short-circuitingelectrode are disposed alternately, and for direction of polarizationthe electrodes are disposed in every pair alternately in the counterdirection, thus the set coming in four electrodes. Here, a mechanicaltravelling wave in which the four electrode patterns 9a to 9d form onewave length is generated by impressing signals 90° different in phase intime on the outer periphery short-circuiting electrode and the innerperiphery short-circuiting electrode.

As described above, sources for generating the two standing wavesdifferent in phase in time do not come one-sided to a semicircle eachlike FIG. 4 but are disposed uniformly with each other at every 1/4wavelengths covering the overall circumference like FIG. 11, therefore auniform travelling wave is generated covering the overall circumference.

According to the aforementioned construction, a mechanical travellingwave can be generated simply by mounting two lead wires regardless ofthe number of waves, and two standing waves can be generated uniformlyaround the whole piezoelectric element, therefore a uniform travellingwave is generated, waves spurious and will not be observed Consequently,the electrical-mechanical conversion efficiency is enhanced, the numberof lead wires is minimized and the structure is simplified, thereforerequirements for miniaturization and curtailment of the productionprocess number may be attained advantageously thereby. FIG. 12(b) showsanother electrode pattern of the piezoelectric transducer in whichcircular blank portions 16 and 17 are provided at the outermostperiphery and the periphery of the central hole of the piezoelectrictransducer respectively in order to prevent leakage current between theboth sides and spark current at the time of applying high voltage forevaporating polarization process derived from excess electrodematerials.

If the blank portions 16 and 17 are provided as described above, theback side may have a wholly covering electrode.

If a blank portion 18 is provided at the outermost periphery on the backside as shown in FIG. 12(a), the blank portion 16 on the front side maynot be required.

FIG. 13 shows another electrode pattern of the piezoelectric transducerin which the outer short circuit electrode has a marking portion 19. Themarking portion may be also provided on the inner short-circuitelectrode. The marking portion is used to distinguish the polarizeddirection of each electrode at the time of the polarization process andat the time of connecting the lead wires.

FIGS. 14(a) and 14(b) show a process of evaporating electrodes shown inFIG. 13 on the piezoelectric transducer. Before the polarization processin FIG. 14(a), divided electrode patterns 20a to 201 are evaporated onthe piezoelectric transducer by using a suitable mask. The dividedelectrode patterns 20a, 20c, 20e, 20g, 20i, 20k are elongated at theouter periphery. On the other hand the remaining electrode patterns 20b,20d, 20f, 20h, 20j, 201 are elongated at the central hole. Two electrodepatterns 20b and 20h which are opposite to each other have widerportions respectively at the inner end point in consideration of slightrotation of the piezoelectric transducer at the time of evaporation ofthe electrodes after polarization process.

The pattern may be constructed of a crom film as contact material to thepiezoelectric material, a nickel film covering the crom film to effectsoldering the lead wire and a gold film covering the nikel film toprevent oxidization and to effect conductivity.

After the polarization process, in FIG. 14(b), outer electrode patterns21a to 21f and inner peripheral patterns 22a, 22b are evaporated torealize the electrode structure shown in FIG. 13.

FIG. 15 is a longitudinal sectional view representing another embodimentof the travelling-wave motor relating to the invention. As in the caseof FIG. 1, a central support rod 1 is unified with a ground way 2through screwing or driving, and further a vibrator part 3 is integralin structure with the central support rod 1 at the central portion, thusrealizing a center-fixed support structure. What is characteristic ofthe embodiment is that a toothed displacement enlarging mechanism 4a isprovided at the output extracting position where the vibrator part 3 anda moving body 6 come in contact to translate the travelling wavecomponent into a rotational motion. Generally, a maximum value Umax ofthe lateral speed component of an elliptic path contributing to arotational motion of the moving body 6 is expressed as:

    Umax=-2π.sup.2 fξ(T/λ)

f: driving frequency

ξ: longitudinal amplitude

T: thickness of vibrator

λ: travelling wave length

therefore, the thickness of the vibrator will have to be increased so asto enhance the rotational frequency. However, a mechanical stiffnessexcessively increases from merely intensifying the thickness, and theresonance frequency also gets high. Accordingly, it is advisable thatthe toothed displacement enlarging mechanism 4a which is rugged in strapperipherally of the vibrator part 3 be provided. It is then preferablefor the motor efficiency that the displacement enlarging mechanism 4a beset in position radially of the vibrator part 3 at about 2/5r≦a≦4/5r asdescribed hereinbefore. Further, the displacement enlarging mechanism 4amay be unified in structure with the vibrator part 3, however, suchtoothing work will entail a high cost, therefore the displacementenlarging mechanism 4a will be prepared separately and then unified withthe vibrator part 3 later. In this case, the displacement enlargingmechanism 4a may also be formed solidly of plastic. Then, different fromthe platelike pressure regulating spring structure in FIG. 1, apressurizing mechanism for this moving body 6 in the embodiment israther compact and comprises a stopper 9 fittable on the central supportrod 1, a pressure regulating spring 7 consisting of a cross spring orthe like, a washer 12 working also as a pressure regulator and others.

FIG. 16 represents a concrete example of the displacement enlargingmechanism, wherein a displacement enlarging mechanism 4a toothed withgrooves arranged in strap at equal intervals therefore is realized at aportion halfway radially of a vibrator part 3. In this case, if theinterval of the grooves is excessively expanded, then a contact areawith the moving body decreases and thus the rotational frequency andtorque will be thus decreased. Further, if the tooth is kept so highlongitudinally, the tooth itself will provide a vibration mode, thedisplacement enlarging mechanism 4a thus loses the function as a rigidbody, thereby leading to a deterioration of the motor efficiency. Thethickness of the disk portional inside the displacement enlargingmechanism 4a may be thinner than that of outside portion a2 to effecthigh efficiency of the motor.

FIG. 17 is a sectional view of the travelling-wave motor according tothe invention using an electrode structure of the piezoelectrictransducer shown in FIG. 11, wherein a vibrator part 3 having thepiezoelectric transducer 5 bonded thereto is supported on a centralsupport rod 1 through driving or the like, and the central support rod 1is fixed on a ground way 2. A moving body 6 is incorporated from overthe vibrator with the central support rod 1 as a guide and pressed ontothe vibrator part 3 by a pressure spring 7 thereon. One 14a of two leadwires 14 is mounted on one part of the outer periphery short-circuitingelectrodes 9a, 9c, 9e in FIG. 11, and another 14b is mounted on one partof the inner periphery short-circuiting electrodes 9b, 9d, 9f throughsoldering or the like. Here, the vibrator generates a mechanicaltravelling wave and the moving body 6 pressed onto the vibrator part 3rotates from impressing signals 90° different in phase in time on thetwo lead wires 14.

The breadth of the circuit projection 8 of the moving body 6 may benarrower than that of the tooth-like projection of the displacementenlarging mechanism 4a since if the material of the moving body issofter than that of the displacement enlarging mechanism 4a, the contactportion of the moving body is worn away.

The displacement enlarging mechanism 4a is set in a position radially ofthe vibrator part 3 at about 2/5r≦ a≦4/5r as described hereinbefore.

FIG. 18 shows one example of impedance characteristic of thetravelling-wave motor shown in FIG. 17 at the time of applying highvoltage between one of the lead wires and the vibration body 3. Theimpedance characteristic is measured under condition that the movingbody 6 is detached from the main body. The motor is as specified below.

    ______________________________________                                        vibration   radial         primary                                            mode        cicumferential wave number 3                                      vibrator    Material       Aluminum                                           body        Outside dia.   10 mm                                                          Thickness      1 mm (2.2 mm at                                                               the projection)                                    piezoelectric                                                                             Outside dia.   10 mm                                              transducer  Thickness      0.1 mm                                                         Piezoelectric Const.                                                                         130 × 10.sup.-12 C/N                                     mechanical Q value                                                                           1500                                               ______________________________________                                    

It is understood from the figure that spurious vibration is not observedexcept at the main resonance point.

The travelling-wave motor shown in FIG. 17 is represented as anequivalent electrical circuit shown in FIG. 19. In this figure, 23, 24,25, 26 and 27 represent the serial impedance, serial capacitance, serialresistance parallel capacitance and load resistance respectively. Thevalue of R1 represents the loss in the travelling motor, e.g. internalloss of the vibrator and mechanical loss at the supporting portion.

Thus, the value of R1 represents the efficiency of the electrodestructure of the piezoelectric vibrator.

The equivalent constants of the travelling-wave motor shown in FIG. 17using the electrode structure shown in FIG. 11 and the travelling-wavemotor having the same construction shown in FIG. 17 using the priorelectrode structure shown in FIG. 6 are described below.

    ______________________________________                                                C0 (nF) L1 (H)  C1 (nF)  R1 (Ω)                                                                        Q                                      ______________________________________                                        Electrode 2.8       0.25    0.0085  82   2080                                 structure                                                                     in FIG. 11                                                                    Electrode 1.8       0.36    0.0055 175   1450                                 structure                                                                     in FIG. 6                                                                     ______________________________________                                    

The R1 value of the electrode structure shown in FIG. 11 is about halfof the prior one shown in FIG. 6.

It is understood from the about R1 values that the electrode structureshown in FIG. 11 is more efficient than that shown in FIG. 6.

FIG. 20 shows one example of the frequency-rotation frequencycharacteristic of the travelling-wave motor shown in FIG. 17 using theelectrode structure shown in FIG. 11. The characteristic is measuredunder the condition that the driving voltage is a 6 Vp-p sine wave, thecontact pressure of the moving body to the vibrating body is about 10gf. It is understood from the figure the rotation frequency is varied ina relatively wide range and the maximum rotation frequency is over 3000r.p.m. and, a high efficiency operation may be realized on the thin andsmall-sized travelling-wave motor according to the motor structurerelating to the invention.

The travelling-wave motor according to the invention may ensure aneffect in realizing a high efficiency operation on a thin andsmall-sized structure through a simple construction wherein a vibrationpart is locked and supported on the central support rod installed on aground way, disposed so as to come in pressure contact at an outputextracting position set at an inside portion coming near to outermostperiphery of the vibrator part, and a driving frequency is set forexcitation in a primary vibration mode radially of the vibrator part.

Accordingly, the travelling-wave motor may be utilized in the field ofprecision equipment. For example, when employed as a motor of anelectronic timekeeper, an advantage never realized in the prior art maybe secured such that a gear train can be curtailed in number and areversible drive is realizable for the low-speed high torque free frombeing influenced by magnets, and that a disturbance will hardly exert aninfluence for the high holding torque.

What is claimed is:
 1. A travelling-wave motor utilizing flexibletravelling waves generated in a vibrating body for driving a movablebody comprising:a ground way for fixing said travelling motor, saidground way having a supporting means; a vibrating body secured andsupported in such a manner that said vibrating body is integrated withsaid supporting means; a piezoelectric vibrator secured to one side ofsaid vibrating body for exciting travelling waves in a primaryoscillation mode with respect to the radial direction in said vibratingbody; a movable body provided on said vibrating body; an annularprojection provided on one of said vibrating body and said movable bodyso that said vibrating body comes into contact with said movable bodythrough the projection at a portion inside of the outermost periphery ofsaid vibrating body; and a pressure-regulator provided on said movablebody for generating suitable contact pressure between said movable bodyand said vibrating body.
 2. A travelling-wave motor as claimed in claim1 wherein said supporting means is constituted by a support shaft whichacts a center of rotation of the movable body.
 3. A travelling-wavemotor as claimed in claim 2 wherein said pressure-regulator is fixed tothe shaft.
 4. A travelling-wave motor as claimed in claim 1 wherein saidannular projection is provided on the body.
 5. A travelling-wave motoras claimed in claim 4 wherein said annular projection includes a tootheddisplacement enlarging mechanism.
 6. A travelling-wave motor as claimedin claim 4 wherein said movable body has another annular projection atthe contact position with said projection of vibrating body.
 7. Atravelling-wave motor as claimed in claim 6 wherein the breadth of saidannular projection of the movable body is narrower than that of thevibrating body.
 8. A travelling-wave motor as claimed in claim 4 whereinthe thickness of the vibrating body at a position inside said annularprojection is thinner than that at a position outside said annularprojection.
 9. A travelling-wave motor as claimed in claim 1 whereinsaid supporting means is made from a conductive material.
 10. Atravelling-wave motor as claimed in claim 1 wherein said piezoelectricvibrator is formed in a disk shape and has a central hole.
 11. Atravelling-wave motor as claimed in claim 10 wherein said piezoelectricvibrator has electrode patterns thereon.
 12. A travelling-wave motor asclaimed in claim 11 wherein said electrode patterns include an electrodepattern divided into a plurality of divided electrodes at equalintervals in multiples of 4 and two short-circuit electrode patterns forshort-circuiting so that said divided electrodes are alternatelyconnected with said short circuit electrode patterns to form two sets ofelectrodes.
 13. A travelling-wave motor as claimed in claim 12 whereinsaid piezoelectric vibrator is polarized so that the portions on whichone group consisting of two adjacent divided electrodes are formed arepolarized alternately with positive and negative potentials.
 14. Atravelling-wave motor as claimed in claim 12 wherein said piezoelectricvibrator has a circular blank portion at the outermost peripherythereof.
 15. A travelling-wave motor as claimed in claim 12 wherein saidpiezoelectric vibrator has a circular blank portion at the periphery ofthe central hole.
 16. A travelling-wave motor as claimed in claim 12wherein one of said divided electrodes has a marking pattern.
 17. Atravelling-wave motor utilizing flexible travelling waves generated in avibrating body for driving a moveable body comprising:a vibrating bodymade of an elastic material and having a disk shape; a piezoelectricvibrator having a disk-shaped and secured to one side of said vibratingbody for exciting travelling waves in a primary oscillation mode withrespect to the radial direction in said vibrating body; a moveable bodyprovided on said vibrating body; and electrode patterns provided on saidpiezoelectric vibrator including an electrode pattern divided into aplurality of divided electrodes at equal intervals in multiples of 4 andtwo short-circuit electrode patterns for short-circuiting so that saiddivided electrodes are alternately connected with said short-circuitelectrode patterns to form two sets of electrodes.
 18. A travelling-wavemotor as claimed in claim 17 wherein said piezoelectric vibrator ispolarized so that the portions on which one group consisting of twoadjacent divided electrodes are formed are polarized alternately withpositive and negative potentials.
 19. A travelling-wave motor as claimedin claim 17 wherein said piezoelectric vibrator has a circular blankportion at the outermost periphery thereof.
 20. A travelling-wave motoras claimed in claim 17 wherein said piezoelectric vibrator has a centralhole and a circular blank portion at the periphery of the central hole.21. A travelling-wave motor as claimed in claim 17 wherein one of saiddivided electrodes has a marking pattern.
 22. A travelling-wave motorcomprising:means defining a stationary support; a vibratory memberaffixed to and supported at a center portion thereof by the support andoperable to be excited in a primary vibration mode in which theoutermost periphery thereof undergoes maximum vibrational displacement;exciting means disposed on one side of the vibratory member for excitingthe vibratory member in the primary vibration mode to produce thereincircumferentially travelling surface waves; a moveable member disposedon the other side of the vibratory member; and means for establishingfrictional contact between the vibratory and movable members at alocation radially inwardly of the outermost periphery of the vibratorymember to effectively translate the travelling surface waves produced inthe vibratory member into frictional movement of the movable member. 23.A travelling-wave motor according to claim 22; wherein the means forestablishing frictional contact comprises means defining a projection onat least one of the vibratory and movable members in frictional contactwith the other of the vibratory and movable members.
 24. Atravelling-wave motor according to claim 23; wherein the projection hasat its distal end a set of teeth-like members.
 25. A travelling-wavemotor according to claim 22; wherein the vibratory member has agenerally circular shape; andthe means for establishing frictionalcontact between the vibratory and movable members is located a radialdistance a from the center of the vibratory member according to therelation 2/5r≦a≦4/5r, where r is the radius of the vibratory member. 26.A travelling-wave motor according to claim 22; including means foradjustably setting the contact pressure between the vibratory andmovable members.
 27. A travelling-wave motor according to claim 26;wherein the means for adjustably setting the contact pressure includesspring means resiliently urging the movable and vibratory members intocontact with one another at said location at an adjustably settablecontact pressure.
 28. A travelling-wave motor according to claim 22;wherein the vibratory and movable members have disk shapes; and themeans for establishing frictional contact comprises an annularprojection on at least one of the vibratory and movable members infrictional contact with the other of the vibratory and movable members.29. A travelling-wave motor according to claim 22; wherein the excitingmeans comprises an electrostrictive member of generally disk shapesecured to the one side of the vibratory member, and an electrodepattern on the electrostrictive member and configured to excite theelectrostrictive member to effect excitation of the vibratory member inthe primary vibration mode.
 30. A travelling-wave motor according toclaim 29; wherein the electrode pattern comprises a plurality of groupsexcitation electrodes, the excitation electrodes in each group havingthe general shape of a circular segment.
 31. A travelling-wave motoraccording to claim 30; wherein the excitation electrodes each have anarc length approximately equal to 1/4 of the wavelength of thetravelling waves.
 32. A travelling-wave motor according to claim 30;wherein the electrode pattern further comprises two sets ofshort-circuit electrodes connected to selected ones of the excitationelectrodes.
 33. A travelling-wave motor according to claim 32; whereinone of the sets of short-circuit electrodes is disposed along the radialoutermost periphery of the electrostrictive PG,48 member and the otherof the sets of short-circuit electrodes is disposed along the peripheryof a central hole formed in the electrostrictive member.